JP2006288472A - X-ray ct apparatus and image reconstruction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of obtaining an image of high precision and high resolution by preventing blurring of the image caused by vibration of a bed top panel, etc. <P>SOLUTION: The image data are reconstructed by detecting the position of an X-ray source 15, an X-ray detector 17 or the bed top panel 29 by a position detector 47, obtaining the relative positional information among the X-ray source 15, the X-ray detector 17 and the bed top panel 29 from the actually detected positional information, and correcting X-ray projection data according to the relative positional information. For example, image data are reconstructed using X-ray projection data detected by an X-ray detecting element located at a position displaced by a quantity equivalent to the quantity of displacement of the bed top panel 29 if the bed top panel 29 is displaced with vibration etc. In this way, displacement of the bed top panel 29 can be offset by correcting the X-ray projection data according to the quantity of displacement and reconstructing the image data, and as a result, the image with high precision and high resolution can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to an X-ray CT apparatus that detects the position of an X-ray source, an X-ray detector, a bed top, or the like and reconstructs image data using the position information.

  The X-ray CT apparatus includes a rotating gantry (gantry) and a bed (bed) disposed in the vicinity of the rotating gantry. The rotating gantry is provided with an opening for inserting and removing the subject, and the X-ray source and the X-ray detector are arranged on the rotating gantry so as to be continuously rotatable around the central axis of the opening. It is installed inside. The couch is supported by a couch top for mounting a subject on an upper part of a couch base that can be raised and lowered.

  The X-ray CT apparatus captures a tomographic image of a predetermined site by horizontally moving the bed top plate on which the subject is placed, inserting the subject into the opening of the rotating base, and connecting the X-ray source and the X-ray detector. The imaging part of the subject is positioned at the imaging position to be connected. Then, the X-ray source and the X-ray detector are rotated around the subject, and during this rotation, X-rays are emitted from the X-ray source toward the subject, and the X-ray detector transmits through the subject. X-ray data is detected.

  The X-ray detector is connected to data acquisition electronics (DAS) that is rotated together with the X-ray detector, and this DAS is detected by the X-ray detector at a predetermined timing. Analog electrical signals) are converted into digital data and collected. Data collection timing by the DAS is every time the X-ray source or the like is rotated by a predetermined angle, and the DAS collects data a predetermined number of times while the X-ray source or the like is rotated once around the subject. Collected data for one round from the round of the subject collected by the DAS is sent to the reconstruction processing unit, and the reconstruction processing unit knows the image data of the imaging region based on the given X-ray projection data. Reconfigure with the calculation method.

  In addition, a spiral scan (helical scan) is performed, and an imaging region consisting of continuous parts (for example, a region from the chest to the upper abdomen) is continuously imaged, and an image of an arbitrary part within this region is obtained. An X-ray CT apparatus configured as described above has been proposed and implemented (for example, Patent Document 1). An X-ray CT apparatus capable of performing this helical scan is conventionally configured as follows.

  For example, the imaging start site (for example, the chest) of the set imaging area is positioned at the imaging position in the opening of the rotating base, and the X-ray source and the X-ray detector are continuously rotated at a constant rotational speed while irradiating X-rays. In synchronization with this rotation, the bed top is horizontally moved at a constant speed so as to displace the part located at the imaging position in the direction of the imaging end part (for example, the upper abdomen) of the imaging region, and the X-ray source And the X-ray detector are scanned so that the rotation trajectory is spiral with respect to the subject, and the set imaging region is continuously imaged.

  The rotational speeds of the X-ray source and the X-ray detector are controlled by a control device. Thereby, for example, from the state in which the X-ray source is located directly above the subject (the X-ray detector is located directly below the subject) until the next state in which the X-ray source is located directly above the subject. In addition, the X-ray source and the like move in a spiral relative to the subject, but the DAS collects data for a predetermined number of times.

  Further, the horizontal movement of the couch top is performed at a speed corresponding to the rotational speed of the X-ray source or the like. The rotational speed of the X-ray source or the like and the moving speed of the bed top are controlled by the control device so as to be a constant ratio. The control device calculates the moving speed of the couch top according to the set rotational speed of the X-ray source, and controls the couch top to move horizontally at the moving speed obtained by the calculation.

  In addition, in order to reconstruct image data of an arbitrary part in the imaging region, position information of the couch top with respect to X-ray projection data collected by DAS is necessary. This position information is obtained by a control device. It has been. For example, the control device calculates the position information based on the rotational speed of the X-ray source or the like and the moving speed of the bed top. During the helical scan, the rotational speed of the X-ray source or the like and the moving speed of the top board are constant, so the position information of the bed top board for each X-ray projection data is uniquely obtained. That is, the actual position of the X-ray source, the X-ray detector and the couch top is not detected, and the position information of the couch top with respect to the X-ray projection data is not obtained, but an ideal model (theoretical model). Based on this, the positions of the X-ray source, the X-ray detector and the couch top are obtained. Then, image data is reconstructed using position information calculated based on an ideal model (theoretical model).

  The reconstruction processing unit specifies the position information of the bed top and the X-ray projection data corresponding to the position, and the collected data of the desired part of the circulation (collected data for one round) and the collected data for one round before and after that. Based on the above, the image data of the part is reconstructed by a known calculation method.

  As described above, in the conventional X-ray CT apparatus, the relative positional relationship between the measurement system including the X-ray source and the X-ray detector and the bed top plate on which the subject is placed is the same as the measurement system and the bed top plate. The reconstruction processing unit reconstructs image data based on the relative positional relationship obtained by the calculation.

JP 2004-181069 A

  In a conventional X-ray CT apparatus, the controller is not based on an ideal model (theoretical model), rather than actually measuring the positions of the X-ray source, the X-ray detector, and the couch top. Calculated and determined. According to such a calculation, position information can be easily obtained. However, in the case of helical scan in particular, fine blurring occurs in detected X-ray projection data due to vibrations of a rotating base and a bed. However, the image reconstructed based on the X-ray projection data may become blurred.

  The resolution of X-ray CT apparatuses is increasing, and the resolution of recent X-ray CT apparatuses is required to be 0.5 [mm] or less, for example. When the vibrations of the above-described rotating base and bed are large, it becomes difficult to satisfy the demand for high resolution.

  As described above, in the conventional X-ray CT apparatus, an ideal model (theoretical model) is assumed in which the X-ray source and the X-ray detector smoothly move on an accurate circle under the control of the control device. Therefore, the controller calculates the positions of the X-ray source and the X-ray detector based on the ideal model. Similarly, an ideal model is assumed in which the bed top plate moves accurately under the control of the control device, and the control device calculates the position of the bed top plate based on the ideal model. In this way, an ideal model of the operation of the X-ray source, the X-ray detector, and the couch top is assumed, and based on the ideal model, the measurement system including the X-ray source and the X-ray detector described above. And the relative position of the couch top.

  However, the rotating base and the couch top operate based on different controls, and furthermore, as described above, vibrations and the like are generated on the rotating base and the like, so the actual operation deviates from the ideal model. It is difficult to accurately obtain the relative positional relationship between the measurement system including the X-ray source and the X-ray detector and the couch top. Even if vibration occurs on a rotating platform, etc., it is difficult to accurately determine the relative positional relationship, so the relative position according to the ideal model is not taken into account. As a result, the reconstructed image becomes blurred.

  The influence on the image reconstruction due to the vibration of the X-ray source, the X-ray detector, and the couch top will be described with reference to FIG. FIG. 6 is a front view of the rotary base of the X-ray CT apparatus, showing an X-ray source, an X-ray detector, and a couch top, and the rotary base and the like are omitted. In FIG. 6, the X-ray source and the X-ray detector are rotated in the direction of the arrow A, and the bed top is movable in the direction perpendicular to the drawing.

  For example, when collecting image data of a subject by helical scanning, the bed top plate 29 moves in a direction perpendicular to the drawing under the control of the control device, and at the same time, the X-ray source 15 and the X-ray detector 17 are moved by the subject. Rotate around. In this state, the X-ray beam is emitted from the X-ray source 15 and the X-ray beam transmitted through the subject is detected by the X-ray detector 17.

  First, a case where the bed top plate 29 vibrates will be described with reference to FIG. When vibration or the like does not occur on the couch top plate 29, the couch top plate 29 is maintained at a height indicated by a broken line and is moved in a direction perpendicular to the drawing under the control of a control device (not shown). Shall. The X-ray source 15 and the X-ray detector 17 scan while rotating around the couch top 29 (subject) in the direction of arrow A, and collect continuous X-ray projection data. The reconstruction processing unit (not shown) assumes that the bed top plate 29 is moved reflecting the ideal model, and the X-ray source 15, the X-ray detector 17 and the bed top obtained from the ideal model. Image data is reconstructed from the relative position information of the plate 29 and the X-ray projection data. In this case, since the couchtop 29 represented by the broken line is maintained at a position reflecting the ideal model, a desired image can be obtained without blurring and the like in the reconstructed image.

  However, when vibrations in the vertical direction (in the direction of arrow B) occur on the bed top plate 29, the bed top plate 29 has an original height (represented by a broken line) reflecting an ideal model under the control of the control device. The position is shifted in the direction of arrow B (height represented by a solid line) from the position, and scanning is performed at the shifted position to collect X-ray projection data. Even in the state where the bed top plate 29 is displaced in the vertical direction as described above, the reconstruction processing unit can obtain the bed top plate 29 from the ideal model, assuming that the bed top plate 29 moves. Image data is reconstructed from the relative position information of the X-ray source 15, the X-ray detector 17 and the couch top plate 29 and the X-ray projection data. As described above, since the image data is reconstructed based on the relative position information that is shifted in the vertical direction from the original position, the reconstructed image becomes blurred in the vertical direction.

  A case where vibration occurs in the X-ray source and the X-ray detector will be described with reference to FIG. The case where vibration occurs in the X-ray source 15 and the like is the same as the case of the bed top plate 29. When vibration or the like does not occur in the X-ray source 15 and the X-ray detector 17, the X-ray source 15 and the like are maintained at a position indicated by a broken line by the control of the control device, and the bed top plate 29 (subject) Scanning is performed while rotating around, and continuous X-ray projection data is collected. The reconstruction processing unit assumes that the X-ray source 15 and the X-ray detector 17 are rotated by reflecting an ideal model (ideal rotation trajectory), and the X-ray source 15 obtained from the ideal model. The image data is reconstructed from the relative position information of the X-ray detector 17 and the couch top 29 and the X-ray projection data. In this case, since the X-ray source 15 and the X-ray detector 17 indicated by the broken line rotate reflecting the ideal model, the reconstructed image does not blur and a desired image is obtained. .

  However, when left and right vibrations occur in the X-ray source 15 and the X-ray detector 17, the X-ray source 15 and the X-ray detector 17 are rotated by the original rotation trajectory reflecting an ideal model by the control of the control device. The position is shifted in the direction of arrow C1 or arrow C2 (position indicated by the solid line) from the position indicated by the broken line, and scanning is performed at the shifted position to collect X-ray projection data. As described above, even when the X-ray source 15 and the X-ray detector 17 are rotated in a state shifted in the left-right direction, the reconstruction processing unit is configured so that the X-ray source 15 and the X-ray detector 17 are ideal models ( Image data from the relative position information of the X-ray source 15, X-ray detector 17 and bed top plate 29 obtained from the ideal model and X-ray projection data. Reconfigure. As described above, since the image data is reconstructed based on the relative position information in a state shifted from the original rotation trajectory in the left-right direction, the reconstructed image becomes blurred in the left-right direction.

  As described above, in the conventional X-ray CT apparatus, when the X-ray source, the X-ray detector, or the couch top is deviated from the original ideal trajectory due to vibration or the like, the deviation is caused at the time of image reconstruction. The image data is reconstructed without taking account of the above. As a result, the reconstructed image becomes blurred or shifted by the amount deviated from the original ideal trajectory, and a high-precision and high-resolution image cannot be obtained.

  The present invention solves the above problem, detects the positions of the X-ray source, the X-ray detector and the couch top, obtains their relative positional relationship, and based on the relative positional relationship. An object of the present invention is to provide an X-ray CT apparatus and an image reconstruction method that can obtain a high-resolution image by canceling blurring and the like occurring in an image by reconstructing image data.

  According to the first aspect of the present invention, an X-ray source that exposes an X-ray beam to a subject, and an X-ray detector disposed opposite to the X-ray source with a space in which the subject is disposed. A table top on which the subject is placed, scanning means for scanning the subject by rotating the X-ray source and the X-ray detector around the subject, and the bed Based on the first detector for detecting the position of the top plate and the position information detected by the first detector, the positional relationship between the X-ray source, the X-ray detector and the bed top plate is calculated. And reconstructing means for reconstructing image data from the X-ray projection data obtained by the X-ray detector based on the positional relationship calculated by the computing means. X-ray CT apparatus.

  The invention described in claim 2 is the X-ray CT apparatus according to claim 1, further comprising a second detector for detecting positions of the X-ray source and the X-ray detector, and the calculation. The means calculates a relative position of the X-ray source, the X-ray detector and the couch top, based on position information detected by the first detector and the second detector, The reconstructing means reconstructs image data from the X-ray projection data based on the relative position calculated by the computing means.

  A third aspect of the present invention is the X-ray CT apparatus according to the second aspect, wherein the calculation means is based on position information detected by the first detector and the second detector. The relative displacement between the X-ray source, the X-ray detector and the bed top plate is calculated, and the reconstructing means is configured to calculate the X-ray according to the relative displacement calculated by the computing means. The image data is reconstructed by correcting the projection data.

  A fourth aspect of the present invention is the X-ray CT apparatus according to the third aspect, wherein the X-ray detector is formed by arranging a plurality of X-ray detection elements, and the reconstruction means is configured to perform the relative processing. The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by an appropriate amount of displacement.

  According to a fifth aspect of the present invention, an X-ray source that exposes an X-ray beam to a subject, and an X-ray detector disposed opposite to the X-ray source with a space in which the subject is disposed. And a bed top plate in which the subject is placed and an index material is embedded therein, and the X-ray source and the X-ray detector are rotated around the subject with respect to the subject. Scanning means for performing scanning, reconstructing means for reconstructing image data based on X-ray projection data obtained by the X-ray detector, and the index material from the image data reconstructed by the reconstructing means Calculating means for calculating a displacement amount of the index material, wherein the reconstruction means corrects the X-ray projection data in accordance with the displacement amount of the index material to reconstruct new image data. X-ray CT apparatus.

  A sixth aspect of the present invention is the X-ray CT apparatus according to the fifth aspect, wherein the X-ray detector is formed by arranging a plurality of X-ray detection elements, and the reconstruction means includes the indicator material. The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by the amount of displacement.

  The invention according to claim 7 is an X-ray detector that exposes an X-ray beam to the subject, and an X-ray detector disposed opposite to the X-ray source with a space in which the subject is disposed. A scanning step of scanning the subject by rotating around the bed top on which the subject is placed, a position detecting step of detecting the position of the bed top, and the detected A calculation step for calculating a positional relationship among the X-ray source, the X-ray detector and the couch top based on position information, and the X-ray detector based on the positional relationship calculated in the calculation step A reconstruction step of reconstructing image data from the X-ray projection data obtained by the above method.

  The invention according to claim 8 is the image reconstruction method according to claim 7, wherein in the position detection step, the positions of the X-ray source and the X-ray detector are further detected, and in the calculation step Based on the detected position information, the relative positions of the X-ray source, the X-ray detector and the couch top are calculated, and in the reconstruction step, the relative positions calculated in the calculation step are calculated. The image data is reconstructed from the X-ray projection data based on a specific position.

  A ninth aspect of the present invention is the image reconstruction method according to the eighth aspect, wherein, in the calculation step, the X-ray source and the X-ray source are based on position information detected in the position detection step. A relative displacement between a line detector and the couch top is calculated, and in the reconstruction step, the X-ray projection data is corrected according to the relative displacement calculated in the calculation step, and image data is obtained. It is characterized by reconfiguring.

  A tenth aspect of the present invention is the image reconstruction method according to the ninth aspect, wherein the X-ray detector includes a plurality of X-ray detection elements arranged, and in the reconstruction step, the relative The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by an appropriate amount of displacement.

  According to an eleventh aspect of the present invention, there is provided an X-ray source for exposing an X-ray beam to the subject, and an X-ray detector disposed opposite to the X-ray source with a space in which the subject is disposed. Scanning step for scanning the subject by rotating around the couch top on which the subject is placed and the indicator material is embedded inside, and the X-ray obtained by the X-ray detector A first reconstruction step for reconstructing image data based on line projection data; a calculation step for calculating a displacement amount of the indicator material from the image data reconstructed in the first reconstruction step; And a second reconstruction step of reconstructing new image data by correcting the X-ray projection data in accordance with the amount of displacement of the index material.

  A twelfth aspect of the present invention is the image forming method according to the eleventh aspect, wherein the X-ray detector includes a plurality of X-ray detection elements arranged, and in the reconstruction step, The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by the amount of displacement.

  According to the invention of claim 1 and claim 7, by actually detecting the position of the couch top on which the subject is placed, the positional relationship among the X-ray source, the X-ray detector and the couch top is obtained, By reconstructing the image data from the X-ray projection data based on the positional relationship, a high-accuracy and high-resolution image can be obtained by canceling out shakes and the like that occur in the image due to vibrations generated on the couch top and the like. Can be obtained.

  According to the invention described in claim 2 and claim 8, the positions of the X-ray source and the X-ray detector are actually detected, and the relative positions of the X-ray source, the X-ray detector and the couch top are determined. By correcting the X-ray projection data based on the relative position and reconstructing the image data, it is possible to cancel out shakes and the like generated in the image due to vibrations generated on the bed top and the like. An image with a resolution can be obtained.

  According to the invention of claim 3 and claim 9, the relative displacement among the X-ray source, the X-ray detector and the bed top plate is obtained, and the X-ray projection data is corrected according to the relative displacement amount. By reconstructing the image data, it is possible to obtain a high-precision and high-resolution image by canceling out blurs and the like generated in the image due to the displacement.

  According to invention of Claim 4 and Claim 10, X-ray projection detected by the X-ray detection element in the position shifted | deviated by the relative displacement amount between X-ray source, X-ray detector, and a bed top plate By reconstructing the image data using the data, it is possible to obtain a high-accuracy and high-resolution image by canceling blurring and the like generated in the image due to the displacement.

  According to the fifth and eleventh aspects of the present invention, when the index material is embedded in the bed top plate and the tomogram is reconstructed by photographing in that state, the index material is copied to the image data. A displacement amount from an ideal model (original position) of the index material in the reconstructed image is obtained, and X-ray projection data is corrected according to the displacement amount to reconstruct new image data. Since the displacement reflects the displacement (deviation) from the ideal model (original position) of the couch top, the X-ray projection data is corrected according to the displacement and the image data is reconstructed. Thus, it is possible to obtain a high-accuracy and high-resolution image by canceling out blurs and the like generated in the image due to the positional deviation of the bed top plate.

  According to the invention of claim 6 and claim 12, by reconstructing the image data using the X-ray projection data detected by the X-ray detection element located at a position shifted by the amount of displacement of the index material, It is possible to obtain a high-accuracy and high-resolution image by canceling blurring and the like generated in the image due to the displacement.

  Hereinafter, an X-ray CT apparatus and an image reconstruction method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5.

(Constitution)
A configuration of an X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of the X-ray CT apparatus according to the embodiment of the present invention, and is a front view of the rotating mount viewed from the front and a side view of the X-ray CT apparatus viewed from the side. FIG. 3 is a diagram showing an X-ray source and an X-ray detector provided in the X-ray CT apparatus according to the embodiment of the present invention.

  As shown in FIG. 1, the X-ray CT apparatus according to this embodiment includes a gantry device, a bed device, and an operation console unit. The gantry device includes a high voltage generator 13, an X-ray source 15, an X-ray detector 17, a rotating gantry 19, a data collection device 21 (DAS), and a gantry driving device 23. Yes. The bed apparatus includes a bed driving unit 25, a bed base 27, and a bed top plate 29. The operation console unit includes a scan control unit 11, a preprocessing unit 31, an X-ray projection data storage unit 33, a reconstruction processing unit 35, an image storage unit 37, an image processing unit 39, an input device 41, A display device 43 and a position information storage unit 45 are provided.

  When scanning by helical scan, the scan control unit 11 sets the rotation speed, slice thickness, fan angle, etc. among the helical scan conditions such as slice thickness and rotation speed input using the input device 41. The control signal is output to the gantry driving device 23 and the bed driving unit 24. The scan control unit 11 outputs an X-ray beam generation control signal for controlling X-ray beam generation to the high voltage generator 13. Further, the scan control unit 11 outputs a detection control signal indicating the detection timing of the X-ray beam to the data acquisition device 21.

  The high voltage generator 13 supplies a high voltage for exposing the X-ray beam from the X-ray source 15 to the X-ray source 15 in accordance with a control signal from the scan control unit 11.

  The X-ray source 15 exposes the X-ray beam with the high voltage supplied from the high voltage generator 13. The X-ray beam exposed from the X-ray source 15 is a fan-shaped or cone-shaped beam. The X-ray source 15 corresponds to the “X-ray source” of the present invention.

  The X-ray detector 17 detects an X-ray beam that is exposed from the X-ray source 15 and transmitted through the subject. In the case of a single slice CT apparatus, the X-ray detector 17 is configured by arranging, for example, 1000 channels of X-ray detection elements in a line in a fan shape or a linear shape. In the case of a multi-slice CT apparatus, the X-ray detector 17 includes a plurality of X-ray detector elements arranged in an array in two orthogonal directions (slice direction and channel direction). It constitutes an X-ray detector. In the case of multi-slice CT, for example, as shown in FIGS. 7A, 7B, and 7C, a plurality of X-ray detection elements 17a are arranged in the slice direction as well as the channel direction. The X-ray detector 17 corresponds to the “X-ray detector” of the present invention.

  The rotary mount 19 (gantry) holds the X-ray source 15 and the X-ray detector 17 inside. Further, the rotating gantry 19 is rotated by a gantry driving unit 23 around a rotation axis passing through an intermediate point between the X-ray source 15 and the X-ray detector 17.

  The data acquisition unit 21 (DAS) has data acquisition elements arranged in an array like the X-ray detection elements 17a of the X-ray detector 17, and the X-ray beam (detected by the X-ray detector 17) Actually, the detection signal) is collected in correspondence with the data collection control signal output by the scan control unit 11. This collected data becomes X-ray projection data.

  When the rotating mount 19 makes one rotation, for example, 1000 times of X-ray projection data is collected, and an image is reconstructed by a method described later based on the X-ray projection data. Note that one data collection is referred to as one view, data of the 1 X-ray detection element 17a in one view and one beam, and all beams in one view (data of all detection elements 17a) are collectively referred to as actual data.

  The gantry driving device 23 rotates the rotating gantry 19 based on the gantry control signal output by the scan control unit 11.

  Based on the bed movement signal output from the scan control unit 11, the bed driving unit 25 obtains the movement amount of the bed top plate 29 per rotation of the rotary mount 19 and moves the bed top plate 29 by this movement amount. . The bed base 27 moves the bed top plate 29 in the vertical direction by the bed driving unit 25. The couch top plate 29 mounts the subject and is movable in the body axis direction (Z-axis direction: slice direction) of the subject.

  The preprocessing unit 31 performs sensitivity correction, X-ray intensity correction, and the like on the X-ray projection data output from the data collection device 21. The X-ray projection data that has been subjected to processing such as sensitivity correction by the preprocessing unit 31 is temporarily stored in the X-ray projection data storage unit 33.

  The reconstruction processing unit 33 reconstructs image data by performing a back projection process on the X-ray projection data stored in the X-ray projection data storage unit 33. This back projection method is the same as a known method. Further, when interpolation processing is performed on X-ray projection data, X-ray projection data at a target slice position is obtained by a known interpolation method such as 360-degree interpolation method or 180-degree interpolation method (opposite data interpolation method). .

  Further, the reconstruction processing unit 33 corrects the X-ray projection data using the position information of the X-ray source 15, the X-ray detector 17 and the bed top plate 29 actually detected by the position detector 47 described later. Processing is performed to correct the displacement (positional deviation) of the bed top plate 29 and the like to reconstruct the image data. The reconstruction processing unit 33 corresponds to “reconstruction means” and “calculation means” of the present invention.

  The reconstructed image data is temporarily stored in the image storage unit 37 and then sent to the image processing unit 39. The image processing unit 39 uses a known method based on the operator's instruction input from the input device 41, and a tomographic image of an arbitrary cross section, a projection image from an arbitrary direction, a three-dimensional image by a rendering process, or the like. Is converted into image data and output to the display device 43. The display device 43 displays the tomographic image output from the image processing unit 39 on the monitor.

  As shown in FIGS. 2 and 3, a position detector 47 is installed in the X-ray CT apparatus according to this embodiment. The position detector 47 is composed of, for example, a non-contact sensor using a laser, an ultrasonic wave, an eddy current or the like, and measures the distance between the position detector 47 and the X-ray source 15 and the X-ray detector. 17 and the position of the couch top 29 are detected. Further, by measuring the acceleration of the X-ray source 15, the X-ray detector 17 and the bed top plate 29 using an acceleration sensor as the position detector 47, the X-ray source 15, the X-ray detector 17 and the bed top plate 29 are measured. The position of is detected. By detecting this position, it becomes possible to detect the displacement of the bed top plate 29 and the like due to vibration and the like. The position detector 47 corresponds to the “first detector” and the “second detector” of the present invention.

  The position information (information indicating vibration) output from the position detector 47 is stored in the position information storage unit 45 in association with the X-ray projection data of each view (each data collection). For example, the position information storage unit 45 performs association based on the detection timing (time). Specifically, position information detected at the same timing (time) at which the X-ray projection data is detected is stored in association with the X-ray projection data. This position information (information indicating vibration) is output to the reconstruction processing unit 35 and used as position information when reconstructing image data from X-ray projection data.

(Operation)
Next, the operation (image reconstruction method) of the X-ray CT apparatus according to the embodiment of the present invention will be described. In this embodiment, a case where a helical scan is executed will be described.

  When performing a helical scan, first, the operator inputs a helical scan condition using the input device 41. The helical scan condition includes information on the range of the imaging region where a tomographic image is desired for the subject. When this imaging area is set, the subject is placed on the couch top 29 so that the scan start side end of this imaging area is the scan start position.

  When the helical scan condition is input, the scan control unit 11 outputs the rotational speed, slice thickness, fan angle, etc. of the helical scan condition to the gantry driving device 23 and the cradle driving unit 25 as a gantry / bed control signal. . The gantry driving unit 23 rotates the rotating gantry 19 at a predetermined rotation speed based on the control signal output from the scan control unit 11. Based on the control signal output from the scan control unit 11, the couch driving unit 25 obtains the movement amount of the couch top plate 29 per rotation of the rotary mount 19 and moves the couch top plate 29 by this movement amount.

  In this state, when a diagnosis start command is input from the input device 41 by the operator, the scan control unit 11 instructs the gantry driving device 23 and the bed driving unit 25 to start diagnosis and controls the generation of X-ray beams. The X-ray beam generation control signal is output to the high voltage generator 13. The high voltage generator 13 generates a high voltage in response to the X-ray beam generation control signal.

  Thereby, the X-ray beam is exposed from the X-ray source 15 and the bed top plate 29 is moved by the bed driving unit 25 so that the relative locus of the X-ray source 15 with respect to the subject becomes spiral. Diagnosis by so-called helical scan is started. When the data acquisition control signal is output from the scan control unit 11, the data acquisition device 21 detects an X-ray beam from the X-ray detector 17 in correspondence with the data acquisition control signal, and detects the detected X-ray. A beam (actually X-ray projection data) is supplied to the preprocessing unit 31.

  Then, the position detector 47 detects the positions of the X-ray source 15, the X-ray detector 17 and the couch top plate 29, and outputs the position information to the position information storage unit 45. The position information storage unit 45 stores position information for each view in association with the X-ray projection data of each view based on the detection timing (time). For example, the position detector 47 detects the vibration of the bed top plate 29 and the like, and outputs the vibration waveform to the position information storage unit 45.

  The reconstruction processing unit 35 reconstructs image data using X-ray projection data collected by scanning. At this time, the reconstruction processing unit 35 reconstructs image data using the relative position information of the X-ray source 15, the X-ray detector 17, and the bed top plate 29 detected by the position detector 47. The reconstruction processing unit 35 reads the position information of the X-ray source 15, the X-ray detector 17, and the bed top plate 29 associated with the X-ray projection data of each view from the position information storage device 45, and the X-ray source 15. Then, the amount of displacement (the amount of displacement) from the ideal model trajectory (original trajectory) of the X-ray detector and the couchtop 29 is calculated.

  Then, the channel in the X-ray detector 17 is shifted by the amount of displacement (the amount of displacement), and the X-ray projection data (ch data) detected by the X-ray detection element in the shift destination channel is used. To create corrected data. The corrected data is reconstructed as image data as X-ray projection data at the position (the position of the ideal model) when there is no displacement (when there is no displacement).

  In this embodiment, the case where the height of the bed top plate 29 deviates from the ideal model trajectory (original trajectory) reflecting the control signal output from the scan control unit 11 while referring to FIG. explain. FIG. 5 is a front view of the rotary mount 19 as viewed from the front, and shows the positional relationship between the X-ray detector 17 and the couch top plate 29.

  In FIG. 5, a state where the bed top plate 29 is in the original trajectory (height) is represented by a broken line, and a state shifted from the original trajectory (height) due to vibration or the like (displaced state) is represented by a solid line. The position detector 47 detects the position (position indicated by a broken line) when the bed top plate 29 is at the original position (height), and outputs the position information to the position information storage device 45. When the bed top plate 29 is displaced in the vertical direction (in the direction of arrow B) due to vibration or the like, the position detector 47 detects a position (a position represented by a solid line) when the bed top plate 29 is displaced, The position information is output to the position information storage device 45. Thus, the position detector 47 detects the position of the bed top plate 29 before and after displacement (before and after displacement).

  The position information of the couch top 29 detected by the position detector 47 is stored in the position information storage device 45 in association with the X-ray projection data of each view.

Then, the reconstruction processing unit 35 reconstructs image data using the X-ray projection data collected by scanning. At this time, the reconstruction processing unit 35 reconstructs image data using the position information of the bed top plate 29 before and after displacement (before and after displacement) detected by the position detector 47. The reconstruction processing unit 35 reads the position information of the bed top plate 29 associated with the X-ray projection data of each view from the position information storage device 45, and calculates the displacement amount (position shift amount) of the bed top plate 29. To do.
Then, the channel in the X-ray detector 17 is shifted by the amount of displacement (the amount of displacement), and the X-ray projection data (ch data) detected by the X-ray detection element in the shift destination channel is used. Create correction data. The correction data is reconstructed as X-ray projection data at the position (the ideal model position) when there is no displacement (when there is no displacement).

  The processing by the reconstruction processing unit 35 will be specifically described. Conventionally, the reconstruction processing unit 35 reconstructs image data based on the position information on the assumption that the couch top plate 29 is at the position of the broken line. The X-ray detection element of the channel corresponding to the position of the broken line is the X-ray detection element 17a, and the reconstruction processing unit 35 detects the X-ray projection data (ch data a) detected by the X-ray detection element 17a. Is reconstructed as X-ray projection data in the imaging region P1 of the subject P. However, in actuality, since the couch top plate 29 is displaced to the position of the solid line, the ch data a is not X-ray projection data reflecting the imaging region P1 of the subject P. As a result, the reconstructed image becomes blurred in the vertical direction.

  In this embodiment, the position detector 47 detects the position of the bed top plate 29 before and after the displacement (before and after the displacement), and the reconstruction processing unit 35 calculates the displacement amount (the amount of displacement). The image data is reconstructed by shifting the ch data by the amount of displacement (the amount of displacement). The X-ray detection element of the channel corresponding to the position of the solid line is the X-ray detection element 17b, and the reconstruction processing unit 35 detects the X-ray projection data (ch data b and the ch data b) detected by the X-ray detection element 17b that is the shift destination. The image data is reconstructed as X-ray projection data in the imaging region P1 of the subject P. Since the X-ray detection element 17b at the shift destination actually detects the X-ray beam transmitted through the imaging part P1 of the subject P, the ch data b becomes X-ray projection data reflecting the imaging part P1 of the subject P. . Therefore, by reconstructing using the ch data b, it is possible to cancel out image blur due to vibration or the like, and it is possible to obtain a highly accurate image.

  Note that the amplitude of the vibration that can be canceled varies depending on the fineness of the arrangement of the X-ray detection elements 17a (b). As the arrangement of the X-ray detectors 17a (b) is made finer, it becomes possible to cancel the vibration corresponding to the vibration having a small amplitude. In addition, when the magnitude of the amplitude that does not affect the reconstruction of the image data is set as a threshold, when the vibration having the amplitude equal to or larger than the threshold is detected, the X detected by the X-ray detector 17a at the position shifted by the amount of displacement is detected. Image data may be reconstructed using line projection data.

  In this embodiment, correction for one beam has been described. However, the same processing is performed for beams at all angles (360 degrees), and all the beams in one view are combined to reconstruct image data.

  As described above, the actual position of the couch top 29 is detected by the position detector 47, the displacement amount due to vibration or the like is calculated from the position, and X-ray projection data necessary for reconstruction is detected from the displacement amount. By selecting an X-ray detection element and reconstructing the image data using the X-ray projection data detected by the selected X-ray detection element, it becomes possible to cancel displacement caused by vibrations, etc. Thus, a high resolution image can be obtained.

  In the present embodiment, the case where the bed top plate 29 is displaced in the vertical direction has been described, but the same applies to the case where the bed top plate 29 is displaced in the slice direction (Z-axis direction) in the multi-slice CT apparatus. By processing, the X-ray projection data can be corrected to obtain a high-precision and high-resolution image. That is, when the couch top plate 29 is also displaced in the slice direction (Z-axis direction), the X-ray projection data detected by the X-ray detection element located at a position shifted in the slice direction (Z-axis direction) by the displacement amount. To reconstruct the image data. As a result, the displacement in the slice direction (Z-axis direction) is canceled out, and an image with high accuracy and high resolution can be obtained.

  In general, in order to improve the resolution of an image, it is necessary to increase the X-ray dose output from the X-ray source 15. However, when the X-ray dose is increased, there is a problem that the exposure amount of the subject increases. In the X-ray CT apparatus according to this embodiment, the X-ray projection data is corrected from the amount of displacement of the bed top plate 29 and the like, so that a high-precision and high-resolution image can be obtained. There is no need to let them. This makes it possible to obtain a high-precision and high-resolution image while reducing the exposure amount of the subject.

  Furthermore, since the relative positional relationship between the subject and the X-ray CT apparatus can be measured by detecting the positions of the X-ray source 15, the X-ray detector 17, and the couch top plate 29, there is a risk in advance. It can also be predicted. For example, even if the subject is likely to be sandwiched between the rotary base 19 and the couch top plate 29, the position of the couch top plate 29 and the like is detected, so that danger is predicted in advance and the couch top plate 29 is detected. It is possible to prevent the subject from being pinched by stopping the driving of the like.

  Note that the X-ray CT apparatus according to this embodiment may be mounted on a PET / CT apparatus or the like in which an X-ray CT apparatus and a nuclear medicine diagnostic apparatus such as a PET apparatus are combined. This makes it possible to accurately perform position comparison with image data of another imaging device such as a PET device.

  In the above-described embodiment, the bed top plate 29 vibrates and the X-ray projection data is corrected from the displacement of the vibration top plate 29 to reconstruct the image data in which the vibrations are canceled. Even when the X-ray detector 17 or the X-ray source 15 vibrates, the displacement of the X-ray detector 17 or the like due to vibration or the like can be canceled by performing the same processing and correcting the X-ray projection data. Thus, it is possible to obtain a high-precision and high-resolution image.

  Further, even when the X-ray source 15, the X-ray detector 17 and the couch top plate 29 are simultaneously vibrating, the relative position (displacement) is detected by detecting the respective positions by the position detector 47. Can be calculated. From the relative position, an X-ray detection element that detects X-ray projection data necessary for reconstruction is selected, and image data is regenerated using the X-ray projection data detected by the selected X-ray detection element. By configuring, displacement due to vibration or the like is canceled out, and an image with high accuracy and high resolution can be obtained.

  In addition, for example, when a mattress is used for the bed top plate 29 and the vibration of the mattress is detected, the vibration absorption amount specific to the mattress is calculated from the value actually detected by the position detector 47. The vibration (displacement) may be obtained by making a difference. For example, vibration may be absorbed by the mattress, and the subject may not vibrate even if the mattress vibrates. In this case, the relative displacement (vibration) of the subject can be obtained by subtracting the vibration absorption amount specific to the mattress from the actually detected value. By correcting the X-ray projection data from the displacement thus obtained and reconstructing the image data, it is possible to obtain an image with high accuracy and high resolution.

  Further, when obtaining the displacement amount of the X-ray source 15 or the X-ray detector 17, a gyroscope may be used as the position detector 47. In this case, a gyroscope is mounted in the rotary mount 19, and the vibration (displacement) of the X-ray source 15 or the X-ray detector 17 is obtained by subtracting the centrifugal force due to the rotation from the rotation angular velocity detected by the gyroscope. Ask. Once the amount of displacement is obtained, the image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at the position shifted by the amount of displacement, as in the above-described processing content, thereby achieving high accuracy. Thus, a high resolution image can be obtained.

  Further, an index material such as a bubble or a metal net may be embedded in the bed top plate 29, and the X-ray projection data may be corrected using this as a mark to reconstruct the image data. As shown in the perspective view of the couch top plate 29 shown in FIG. 4, an index material 29a made of bubbles or a metal net is embedded in the couch top plate 29, and in this state, an X-ray beam is exposed to perform imaging. The indicator material 29a may be anything as long as it is copied in an image reconstructed by exposure to an X-ray beam. Since the reconstruction material represents the index material 29a such as a metal net, the reconstruction processing unit 35 has a displacement amount of the index material 29a from an ideal position based on a control signal from the scan control unit 11 ( The amount of misalignment) is calculated. Then, the reconstruction processing unit 35 reconstructs image data using the X-ray projection data detected by the X-ray detection element located at the position shifted by the displacement amount. By reconstructing the image data in this way, it is possible to cancel out the displacement in the image, so that it is possible to obtain an image with high accuracy and high resolution.

  Further, even when using a gyroscope or using an index material, the amount of displacement of the X-ray source 15, X-ray detector 17 and bed top plate 29 with respect to the beam at all angles is obtained. The image data is reconstructed by combining all the beams.

1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. It is a figure which shows schematic structure of the X-ray CT apparatus which concerns on embodiment of this invention, and is the front view which looked at the rotation mount from the front, and the side view which looked at the side of the X-ray CT apparatus. It is a figure which shows the X-ray source and X-ray detector with which the X-ray CT apparatus which concerns on embodiment of this invention is equipped. 1 is a perspective view of a couch top provided in an X-ray CT apparatus according to an embodiment of the present invention. It is a front view for demonstrating operation | movement of the X-ray CT apparatus which concerns on embodiment of this invention, and is a figure which shows an X-ray detector and a bed top plate. It is a figure for demonstrating the influence on the image reconstruction by the vibration which generate | occur | produces in a X-ray CT apparatus. It is a perspective view which shows the structure of an X-ray detector (X-ray detection element).

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Scan control part 13 High voltage generator 15 X-ray source 17 X-ray detector 17a X-ray detection element 19 Rotating mount (gantry)
21 Data collection device (DAS)
DESCRIPTION OF SYMBOLS 23 Stand drive device 25 Bed drive part 27 Bed base 29 Bed top plate 29a Index material 31 Pre-processing part 33 X-ray projection data storage part 35 Reconstruction process part 37 Image storage part 39 Image processing part 41 Input device 43 Display apparatus 45 Position information storage unit 47 Position detector

Claims (12)

An X-ray source for exposing an X-ray beam to the subject;
An X-ray detector disposed opposite to the X-ray source across a space in which the subject is disposed;
A table top on which the subject is placed;
Scanning means for scanning the subject by rotating the X-ray source and the X-ray detector around the subject;
A first detector for detecting the position of the couch top;
Based on position information detected by the first detector, calculation means for calculating a positional relationship between the X-ray source, the X-ray detector, and the bed top;
Reconstructing means for reconstructing image data from X-ray projection data obtained by the X-ray detector based on the positional relationship calculated by the computing means;
An X-ray CT apparatus comprising: A second detector for detecting a position of the X-ray source and the X-ray detector;
The calculation means calculates a relative position of the X-ray source, the X-ray detector, and the bed top plate based on position information detected by the first detector and the second detector. And
The X-ray CT apparatus according to claim 1, wherein the reconstruction unit reconstructs image data from the X-ray projection data based on a relative position calculated by the calculation unit. The calculation means calculates a relative displacement among the X-ray source, the X-ray detector, and the bed top plate based on position information detected by the first detector and the second detector. And
3. The X-ray according to claim 2, wherein the reconstructing unit reconstructs image data by correcting the X-ray projection data according to a relative displacement calculated by the computing unit. CT device. The X-ray detector is formed by arranging a plurality of X-ray detection elements,
The reconstructing means reconstructs image data using X-ray projection data detected by an X-ray detection element located at a position shifted by the relative displacement amount. X-ray CT system. An X-ray source for exposing an X-ray beam to the subject;
An X-ray detector disposed opposite to the X-ray source across a space in which the subject is disposed;
A table top on which the subject is placed, and an indicator material is embedded therein;
Scanning means for scanning the subject by rotating the X-ray source and the X-ray detector around the subject;
Reconstructing means for reconstructing image data based on X-ray projection data obtained by the X-ray detector;
Calculating means for calculating a displacement amount of the indicator material from the image data reconstructed by the reconstructing means,
The X-ray CT apparatus is characterized in that the reconstructing means reconstructs new image data by correcting the X-ray projection data in accordance with a displacement amount of the index material. The X-ray detector is formed by arranging a plurality of X-ray detection elements,
6. The reconstructing means reconstructs image data using X-ray projection data detected by an X-ray detection element located at a position shifted by an amount of displacement of the index material. X-ray CT system. An X-ray source that exposes the X-ray beam to the subject, and an X-ray detector disposed opposite to the X-ray source across a space in which the subject is arranged are placed on the subject A scan step of scanning the subject by rotating around the bed top;
A position detecting step for detecting the position of the bed top;
A calculation step of calculating a positional relationship between the X-ray source, the X-ray detector, and the bed top plate based on the detected position information;
Reconstructing step of reconstructing image data from X-ray projection data obtained by the X-ray detector based on the positional relationship calculated in the calculating step;
An image reconstruction method comprising: In the position detecting step, the positions of the X-ray source and the X-ray detector are further detected,
In the calculation step, a relative position of the X-ray source, the X-ray detector and the bed top is calculated based on the detected position information,
The image reconstruction method according to claim 7, wherein in the reconstruction step, image data is reconstructed from the X-ray projection data based on the relative position calculated in the calculation step. In the calculation step, a relative displacement between the X-ray source, the X-ray detector and the bed top plate is calculated based on the position information detected in the position detection step,
9. The image reconstruction according to claim 8, wherein in the reconstruction step, the image data is reconstructed by correcting the X-ray projection data in accordance with the relative displacement amount calculated in the calculation step. Method. The X-ray detector is formed by arranging a plurality of X-ray detection elements,
The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by the relative displacement amount in the reconstruction step. Image reconstruction method. An X-ray source that exposes the X-ray beam to the subject, and an X-ray detector disposed opposite to the X-ray source across a space in which the subject is placed, A scan step of scanning the subject by rotating around the couch top embedded with an indicator material;
A first reconstruction step of reconstructing image data based on X-ray projection data obtained by the X-ray detector;
A calculation step of calculating a displacement amount of the indicator material from the image data reconstructed in the first reconstruction step;
A second reconstruction step of reconstructing new image data by correcting the X-ray projection data in accordance with the amount of displacement of the indicator material;
An image reconstruction method comprising: The X-ray detector is formed by arranging a plurality of X-ray detection elements,
The image data is reconstructed using the X-ray projection data detected by the X-ray detection element located at a position shifted by the displacement amount of the index material in the reconstruction step. Image reconstruction method.

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